<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            height: 100px;
            width: 100vw;
        }
        .boxl{
            float: left;
            height: 100px;
            width: 20vw;
            background-color: skyblue;
        }
        .boxr{
            margin-left: -20vw;
            height: 100px;
            background-color: yellow;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="boxl"></div>
        <div class="boxr"></div>
    </div>
</body>
<script>
    fun = function(){
        
    }
    console.log(fun.prototype.toString);
</script>
</html>